JP3432091B2 - Scanning electron microscope - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning electron microscope equipped with an electrostatic objective lens and capable of efficiently detecting electrons from a sample.

[0002]

2. Description of the Related Art FIG. 1 shows a main part of a scanning electron microscope using an electrostatic objective lens. In this figure, 1 is an inner tube arranged along the optical axis O of the electron beam,
A high voltage of several kV is applied to the inner tube 1 from a high voltage power supply 2. Below the inner tube 1, a lower electrode 3 of the objective lens, which is connected to the ground side of the high voltage power supply 2, is provided.

A sample 4 is provided below the lower electrode 3 of the objective lens.
Is provided, but this sample is also at earth potential. A donut-shaped electron detector 5 is arranged inside the inner tube 1. Also, the inner tube 1
Two-stage deflection coils 6 and 7 are provided on the outer side of, and although not shown, two-dimensional scanning signals are supplied to the deflection coils 6 and 7 from an arbitrary scanning circuit.

The signal detected by the electronic detector 5 is
It is supplied to the video image generation circuit 8, and the circuit 8 adjusts contrast and brightness. In addition, the generation circuit 8 has
A frame memory is provided so that the image signals are integrated to improve the SN ratio. The image signal from the video image generation circuit 8 is supplied to a monitor device 9 such as a cathode ray tube. The operation of such a configuration will be described below.

The primary electron beam EB generated and accelerated by an electron gun (not shown) travels inside the inner tube 1 and is irradiated onto the sample 4 while receiving a lens action by a focusing lens (not shown) at several stages. It At this time, since a high voltage is applied to the inner tube 1 from the high voltage power source 2 and the lower electrode 3 of the objective lens is set to the ground potential, the inner tube 1 is decelerated between the lower electrode 3 and the inner tube 1. , Is focused on the sample 4 at earth potential.

The focused primary electron beam EB is reflected by the sample 4
Secondary electrons e are emitted from the. The emitted secondary electron e is
It is accelerated upward by the electric field between the lower end of the inner tube 1 and the lower electrode 3 of the objective lens. The accelerated secondary electrons e are absorbed and detected by the electron detector 5 located just above the lower end of the inner tube 1.

The signal detected by the electronic detector 5 is supplied to the video image generating circuit 8 and subjected to appropriate contrast adjustment and brightness adjustment. The signal subjected to various adjustments is supplied to a monitor device 9 such as a cathode ray tube which is scanned in synchronization with the scan signals to the scan coils 6 and 7, and a secondary electron image is displayed on the monitor device 9. .

FIG. 2 shows a main part of another example of a scanning electron microscope using a conventional electrostatic objective lens, and the same components as those in FIG. 1 are designated by the same reference numerals. In this conventional example, a part of the inner tube 1 is formed in the shape of a mesh 10, and the same high voltage as that of the tinner tube 1 is applied to the mesh portion 10. Further, in this example, the electron detector 11 is arranged outside the mesh 10.

In the structure of FIG. 2, the secondary electrons e emitted from the sample 4 are accelerated upward by the electric field between the lower end of the inner tube 1 and the lower electrode 3 of the objective lens, and a part of the inner tube 1 is emitted. It goes to the outside of the tube 1 through the mesh part 10 provided in the tube, and is detected by the electron detector 11. The detection signal of the electronic detector 11 is supplied to the video image generating device 8 shown in FIG.

[0010]

In the conventional apparatus shown in FIG. 1, when the electron detector 5 is located just above the lower end of the inner tube 1, the deflection coils 6 and 7 deflect the primary electron beam EB, so It is necessary to provide a large diameter hole at the center of the detector 5. Therefore, many secondary electrons e pass through this hole and do not enter the detector 5, so
The detection efficiency of secondary electrons becomes poor. As a result, there arises a problem that the image quality of the secondary electron image displayed on the monitor 9 is deteriorated.

Also, the electric field strength generated between the lower end of the inner tube 1 which is the objective lens and the lower electrode 3 changes the trajectory of the secondary electrons, which causes a problem that the brightness of the image quality is not constant.

Furthermore, because of the structure in which the electron detector 5 is located immediately above the lower end of the inner tube, the electron detector 5 cannot use a scintillator or an optical transmission line, which makes the structure large, and the electron multiplier 5 has a porous surface. Microchannel plates are commonly used. However, the microchannel plate has a drawback that the porous surface is filled with contamination and the detection efficiency gradually decreases.

In the conventional apparatus shown in FIG. 2, the secondary electrons e generated from the sample 4 and deflected by the objective lens pass through the mesh portion 10 and are detected by the electron detector 11 arranged outside the mesh 10. Although detected, in this method, the trajectory of the secondary electrons changes depending on the electric field strength of the objective lens, so that the brightness of the image does not become constant but changes temporally. As a result, a stable image cannot be obtained for a long time, and the secondary electron detection efficiency is poor.

Further, in any of the conventional devices shown in FIGS. 1 and 2, when a sample such as a semiconductor sample which is easily charged up is observed, the image is distorted due to the influence of the charge up
Furthermore, in an extreme case, a phenomenon occurs in which secondary electrons cannot escape from the sample 5. Then, it is not possible to efficiently detect the electrons emitted from the bottom of the contact hole formed on the semiconductor sample surface and having a high aspect ratio.

The present invention has been made in view of the above circumstances, and an object thereof is to detect electrons from a sample efficiently even if it is a sample such as a semiconductor sample that is easily charged up, and has a high resolution. It is to realize a scanning electron microscope capable of obtaining an image.

[0016]

According to another aspect of the present invention, there is provided a scanning electron microscope which focuses a primary electron beam on a sample by an electrostatic lens type objective lens and two-dimensionally focuses the primary electron beam on the sample. In a scanning electron microscope that scans and detects electrons from the sample to obtain a scan image of the sample,
A high voltage is arranged an inner tube which is applied along the optical axis of the primary electron beam, a detector for detecting electrons from the sample to the interior of the inner tube is provided, generated from the sample vertebral
Among the secondary electrons and reflection electrons toward the inside of emissions toner tube detector direction, secondary electrons towards the detector is absorbed by colliding with the inner wall of the inner tube in the middle, detector position only reflections electrons incident It is characterized in that it has placed a.

[0017]

[0018]

[0019]

[0020]

[0021]

According to the first aspect of the invention, an inner tube to which a high voltage is applied is arranged along the optical axis of the primary electron beam, and a detector for detecting electrons from the sample is provided inside the inner tube. of generated secondary electrons and reflected electrons, almost all of the secondary electrons towards the detector is absorbed by colliding with the inner tube, only reflection electrons to the detector is incident.

A scanning electron microscope according to a second aspect of the present invention is a deflecting means for scanning a primary electron beam on a detector.
It is characterized by being placed on the upper side. According to the second aspect of the invention, the detector is arranged above the deflecting means for scanning the primary electron beam, and the electron detection area of the detector is increased to enhance the detection efficiency.

The scanning electron microscope according to the invention of claim 3 is characterized in that an electromagnetic field superposition type objective lens is used as the objective lens. According to the invention of claim 3, an electromagnetic field superposition type objective lens is used as the objective lens, and the aberration of the objective lens is reduced.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 3 shows a main part of the scanning electron microscope according to the present invention, but the same or similar components as in FIG. 1 are assigned the same reference numerals and detailed explanations thereof are omitted.

In the embodiment shown in FIG. 3, a doughnut-shaped scintillator 12 is arranged perpendicular to the optical axis of the primary electron beam inside the inner tube 1 to which a high voltage of several kV is applied from the high voltage power source 2. ing. This scintillator 1
2 is connected to the inner tube 1 and has the same potential as the inner tube 1.

Although the scintillator 12 is held in close contact with the lower surface of the photoconductive path 13, the photoconductive path 13 has a hole for allowing the primary electron beam EB to pass therethrough. A conductive elongated pipe 14 is inserted along the optical axis. The upper side of the light conducting path 13 is about 45 °
Is cut at an angle of, and the cut surface is mirror-finished and then metal-coated 15. The metal coating 15 has a function of preventing the primary electron beam EB from directly colliding with the insulating photoconductive path 13 and causing charge-up on the surface of the photoconductive path 13.

The light generated by the scintillator 12 is reflected in the direction of 45 ° by the surface of the metal coating 15 and passes through the photoconductive path 13. A phototube 16 such as a photomultiplier tube is provided on the exit side of the photoconductive path 13, and the scintillator 12
The light generated in 1 is detected by the phototube 16. The signal detected by the phototube 16 is supplied to the monitor 9 via the video image generation circuit 8.

The scintillator 12 is arranged above the positions of the deflection coils 6 and 7. As a result, in the portion of the scintillator 12 and the photoconductive path 13, the primary electron beam EB travels straight along the optical axis, and the electron beam passage hole of the photoconductive path 13, the pipe 14, and the electron beam passage hole of the scintillator 12 are respectively formed. The diameter of can be significantly reduced. The operation of such a configuration will be described below.

The primary electron beam EB generated and accelerated by an electron gun (not shown) is focused by the focusing lenses of several stages and enters the inner tube 1. A high voltage of, for example, about 8 kV is applied to the inner tube 1 from the high voltage power source 2, and as a result, the primary electron beam EB is accelerated when entering the inner tube 1.

The accelerated primary electron beam EB passes through the pipe 14 provided in the electron beam passage hole of the photoconductive path 13 inserted in the inner tube 1, and the lower end of the inner tube 1 and the ground of the high voltage power supply 2 are grounded. The sample 4 is focused by the decelerating electric field generated between the lower electrode 3 of the objective lens connected to the side.

Primary electron beam EB focused on sample 4
Causes secondary electrons e and reflected electrons r to be emitted from the sample.
The emitted secondary electrons e and reflected electrons r are accelerated upward by the electric field generated between the lower electrode 3 of the objective lens and the lower end of the inner tube 1.

Since the secondary electrons e emitted from the sample have a small energy immediately after being emitted from the sample, they undergo a strong lens action by the above-mentioned electric field, and most of them are in the scintillator 12 located relatively above the inner tube 1.
However, the inner wall of the inner tube 1 collides with and is absorbed.

On the other hand, the reflected electrons r emitted upward from the sample have almost the same energy immediately after being emitted from the sample 4 as the energy of the primary electron beam.
The lens action received by the electric field is small, and when further accelerated, the lens travels substantially straight inside the inner tube 1 and collides with the surface of the scintillator 12 located relatively above in the inner tube 1.

Reflected electrons r colliding with the scintillator 12
Causes the scintillator 12 to emit light. Scintillator 12
The light from is reflected by the surface of the metal coating 15 having a surface with an inclination angle of about 45 ° in a direction approximately perpendicular to the optical axis.
The reflected light passes through the photoconductive path 13 and the photoconductive path 1
It is converted into an electric signal by the phototube 16 which is arranged close to the end of 3. The detection signal of the photoelectric tube 16 is supplied to the video image generation circuit 8 similar to that in FIG. Since the video signal from the video image generation circuit 8 is supplied to the monitor 9,
A scan image of the sample is displayed on the monitor 9.

FIG. 4 shows a potential curve E generated between the inner tube 1 to which a high voltage is applied from the high voltage power source 2 and the objective lens lower electrode 3, and an electron trajectory R of the primary electron beam EB due to the lens action by this electric field. Is shown. The primary electron beam is diverged and focused by the decelerating electric field.

FIG. 5 shows the generation process of the secondary electrons e and the reflected electrons r when the primary electron beam is incident on the sample 4. The primary electron beam EB penetrates into the inside of the sample 4 due to its energy level and repeats interaction with the electrons in the sample 4. A region where electrons repeatedly interact with each other is called an electron dissipation region S, and secondary electrons e and backscattered electrons r are emitted to the outside of the sample 4 from an upper region of about 1/3 thereof.

Particularly, the area where the secondary electrons e are generated is called an electron escape area λ, and the secondary electrons e are emitted from a relatively shallow area, so that the secondary electrons e have fine information on the sample 4. It will be. Further, when the accelerating voltage is 3 kV or less, the electron dissipation region S also becomes small and the generation region where the reflected electrons r are emitted approaches the electron escape region λ of the secondary electrons e, so that the reflected electrons r are also fine on the sample 4. Get to have the information.

FIG. 6A shows a cross section of the contact hole 21 formed on the sample 4 and having a high aspect ratio. As is well known, the aspect ratio is the ratio of the hole diameter to the hole depth. In this case, even if the primary electron beam EB reaches the bottom of the contact hole 21, most of the generated secondary electrons e do not enter the bottom of the contact hole 21 and thus collide with the sidewall of the contact hole 21. I will end up.

On the other hand, the reflected electrons r emitted in a substantially vertical direction travel straight in the contact hole, and
Since it can be emitted from the surface of the contact hole, if the reflected electrons r can be detected, it is possible to observe the bottom of the contact hole having a high aspect ratio.

Further, as shown in FIG. 6B, in the sample 4 which is easy to be charged like the semiconductor sample, the negative charges are accumulated on the surface of the sample 4 and the secondary electrons e generated from the bottom of the contact hole 21 are generated. , Its energy is too low to reach the surface of the sample 4. However, the reflected electrons r emitted in the vertical direction with high energy are
If the backscattered electrons r can be emitted from the surface of the contact hole 21 and the bottom of the contact hole 21 can be observed in the same manner.

As described above, in the configuration of FIG. 3, the scintillator 12 is arranged relatively above the inner tube 1 so that the secondary electrons e emitted from the sample are absorbed by the inner tube 1 and almost only the reflected electrons r are absorbed. Since it is configured to detect, the information on the bottom of the sample having a high aspect ratio can be stably detected.

Further, since the scintillator 12 is arranged above the position of the deflection coils 6 and 7, the scintillator 1
2 and the portion of the photoconductive path 13 may be provided with an electron beam passage hole through which the primary electron beam EB traveling straight along the optical axis can pass. As a result, the number of backscattered electrons r passing through the electron beam passage hole can be extremely reduced, and most of the backscattered electrons can be made incident on the scintillator 12. Therefore, the detection efficiency of the backscattered electrons can be greatly improved.

Further, since the scintillator is used as the means for detecting backscattered electrons, it is possible to avoid the problem that the porous surface is buried due to contamination and the detection efficiency is lowered, unlike the conventional microchannel plate.

FIG. 7 shows another embodiment of the present invention. In the example of FIG. 7, an electromagnetic field superposition type objective lens is used as the objective lens. That is, the magnetic field lens 25 is arranged at the lower end portion of the inner tube 1, and the magnetic pole of the magnetic field lens 25 is connected to the ground side of the high voltage power supply 2.

In this structure, the objective lens action is achieved by the magnetic field of the magnetic field lens 25 and the electric field of the electrostatic lens between the inner tube 1 and the magnetic pole of the magnetic field lens 25. Since the electromagnetic field superposition type objective lens can reduce the aberration, it is effective in obtaining a higher resolution image. The configuration for detecting backscattered electrons from the sample 4 and the mechanism for detecting backscattered electrons are the same as those in the embodiment shown in FIG.

Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments. For example, although a detection system mainly including a scintillator was used for detecting backscattered electrons, another detection system such as a microchannel plate can be used as long as the influence of contamination is small. Further, it is possible to further improve the image quality by using it together with other secondary electron detectors.

[0048]

As described above, according to the first aspect of the invention, the inner tube to which a high voltage is applied is arranged along the optical axis of the primary electron beam, and electrons from the sample are detected inside the inner tube. Generates from the sample by installing a detector to
Of the secondary electrons and reflected electrons that go to the detector
Almost all of the
Therefore , the detector is configured so that only the reflected electrons are incident .

[0049]

[0050]

[0051]

[0052]

As a result, the electrons from the sample can be efficiently detected. In addition, in the case of this configuration, mainly when the reflected electrons from the sample are selectively incident on the detector and the sample is a sample such as a semiconductor sample that is easily charged up, when observing a contact hole with a high aspect ratio. Even in this case, it becomes possible to stably observe the morphology of the sample with high resolution.

According to the second aspect of the invention, since the detector is arranged above the deflecting means for scanning the primary electron beam, the electron detection area of the detector can be increased and the detection efficiency can be improved.

According to the third aspect of the invention, since the electromagnetic field superposition type objective lens is used as the objective lens, the aberration of the objective lens can be reduced, and a high resolution scanning electron microscope is provided.

[Brief description of drawings]

FIG. 1 is a diagram showing a scanning electron microscope using a conventional electrostatic objective lens.

FIG. 2 is a diagram showing a scanning electron microscope using a conventional electrostatic objective lens.

FIG. 3 is a diagram showing a main part of a scanning electron microscope according to the present invention.

FIG. 4 is a diagram showing a potential curve of an electrostatic objective lens and a trajectory of a primary electron beam.

FIG. 5 is a diagram showing how secondary electrons and reflected electrons are emitted from a sample by irradiation with a primary electron beam.

FIG. 6 is a diagram showing how reflected electrons and secondary electrons are emitted from a contact hole.

FIG. 7 is a diagram showing another embodiment of the present invention using an electromagnetic field superimposing type objective lens.

[Explanation of symbols]

1 inner tube 2 high voltage power supply 3 Lower electrode of objective lens 4 samples 6,7 deflection coil 8 Video image generation circuit 9 monitors 12 scintillator 13 Optical path 14 pipes 15 Metal coating 16 Phototube

Continuation of front page (56) Reference JP-A-8-203459 (JP, A) JP-A-5-266855 (JP, A) JP-A-3-283249 (JP, A) JP-A-8-138611 (JP , A) JP 8-321273 (JP, A) JP 8-64163 (JP, A) JP 4-370640 (JP, A) JP 64-10561 (JP, A) JP 3-22339 (JP, A) JP 8-138612 (JP, A) JP 7-6726 (JP, A) JP 6-243814 (JP, A) JP 6-68832 (JP, A) JP-A-3-272554 (JP, A) JP-A-8-83589 (JP, A) JP-A-6-117847 (JP, A) JP-A-58-218737 (JP, A) (58) Survey Fields (Int.Cl. ⁷ , DB name) H01J 37/244 H01J 37/28 H01L 21/66

Claims (3)

(57) [Claims] 1. An electrostatic lens type objective lens is used to focus a primary electron beam on a sample, and the primary electron beam is two-dimensionally scanned on the sample to detect electrons from the sample to form a scan image of the sample. In the scanning electron microscope designed to obtain, the inner tube to which a high voltage is applied is arranged along the optical axis of the primary electron beam, and a detector for detecting electrons from the sample is provided inside the inner tube to generate the sample. Shiina
Among the secondary electrons and reflection electrons toward the inside over the tube to the detector direction, secondary electrons towards the detector is absorbed by colliding with the inner wall of the inner tube in the middle, only the reflections electrons incident
Scanning electron microscope, characterized in that it has placed the detector position. 2. The scanning electron microscope according to claim 1, wherein the detector is arranged above the deflecting means for scanning the primary electron beam. 3. The scanning electron microscope according to claim 1, wherein the objective lens is an electromagnetic field superposition type objective lens.